Falls among the elderly can be traumatic and potentially life threatening (see Okuizumi, H., Harada, A, Iwata, H. & Konishi, N. (1998). Effect on the femur of a new hip fracture preventative system using dropped-weight impact testing. Journal of Bone and Mineral Research, 13: 1940-1945, and Wiener, S. L., Andersson, G. B. J., Nyhus, L. M. & Czech, J. (2002). Force reduction by an external hip protector on the human hip after falls. Clinical Orthopaedics and Related Research, 398: 157-168.). Injuries sustained at the hip during a fall can range from minor bruising to more catastrophic fractures of the femur. As a result, the risks of morbidity, disability, long-term institutionalization and death all increase (see for example Cooper, C. Atkinson, E. J., Jacobsen, S. J., O'Fallon, W. M., & Melton, L. J. |I| (1993). Population-based study of survival after osteoporotic fractures. American Journal of Epidemiology, 137: 1001-1005). The occurrence of fractures is associated with a direct impact to the trochanteric area of the hip (see Cummings, S. R. & Nevitt, M. e. (1989). A hypothesis: The causes of hip fractures. Journal of Gerontology. 44: M107-M111, as well as Nevitt, M. C. & Cummings, S. R. (1993). Type of fall and risk of hip and wrist fractures: The study of osteoporotic fractures. Journal of the American Geriatrics Society, 41: 1226-1234), and the severity of the injury is affected by the failing mechanisms, the impact energy during the fall, and the energy absorption of the soft tissue in the surrounding area. One method of preventing or diminishing the severity of injuries during falls is to protect the hip with external padding.
Previous research suggests that hip padding or hip protectors are a viable method of preventing hip fractures. Research suggests that hip protectors may help reduce the incidence of hip fractures by more than 50% (see the articles by Ekman, A, Mallmin, H., Michaelsson, K., & Ljunghall, S. (1997). External hip protectors to prevent osteoporotic hip fractures. Lancet, 350: 563-564, by Kaunus, P., Parkkari, J., Niemi, S. et al. (2000). Prevention of hip fracture in elderly people with use of a hip protector. New England Journal of Medicine, 343: 1506-1513, and by Lauritzen, J. B., Petersen, M. M. & Lund, B. (1993). Effect of external hip protectors on hip fractures. Lancet, 341: 11-13).
Impact protection pads, such as hip protectors, can be understood to fit within two classes of products. The first class of such protection pads, as illustrated in FIG. 1A, have a hard shell that seeks to transfer or redistribute impact energy from a vulnerable area to a surrounding area, and in the case of hip protectors, they attempt to avoid contact with the greater trochanter area of the femur, while engaging the soft tissue surrounding the greater trochanter area. Such protectors can cause bruising and even a tearing of the skin where the rigid shell impacts on the soft tissue. The result can be lead to infection and/or require significant time to heal. This makes for a significant bulge, see for example U.S. Pat. No. 5,557,804 to Ovortrup et al. Such protection pads are effective for their intended purpose, namely to protect the vulnerable body area, however, the comfort of the person wearing the protector is certainly compromised when resting or otherwise applying pressure on the protector.
The second class of such protection pads seek to absorb impact energy generally over the vulnerable area. Again in the case of hip protectors, an example of such a pad is U.S. Pat. No. 4,573,216 to Wortberg. With such devices, as illustrated in FIG. 1B, the object is to provide a comfortable, compliant pad that can be worn, and then on impact can dissipate the impact energy so that peak impact force remains below a lower average breaking threshold of the adult femur. This absorption of the impact energy does involve some spatial redistribution of force, however, due to its essentially flexible and non-rigid structure, the spatial spread out of the impact energy is still over the vulnerable area with only partial distribution onto the surrounding soft tissue, and the spreading of the impact energy is only partly responsible for the reduction in peak impact forces, while the internal absorption of impact within the pad structure temporally spreads out the impact energy and reduces peak impact force.
Also known in the art is a body protection pad, as illustrated in FIG. 1C, that has a number of small fragments of honeycomb covered with and interconnected by a dense foam molded over the fragments to flex at the interfaces of the fragments. Such a pad is manufactured for the motorcycle body armour market by Planet-Knox, Cumbria, United Kingdom. The pads come in a variety of shapes for different body parts. The pad illustrated is the shape designed for the shoulder, and is resold in the UK for use as a hip pad for the elderly. However, a point impact at an interface between fragments of the honeycomb results in potentially greater peak impact than impact in the middle of a fragment. Also, while compliance is good for curving over a knee or elbow, the honeycomb itself does not undergo flexion and compliance as the webbing between fragments and the protected body tissue is more supple than the honeycomb.
For some applications, such as hip protectors, comfort of the protection pad is quite important. The pad is worn on the body preferably both day and night. Removal of the pad exposes the user to the risk of hip fracture, and comfort is important.